The present invention relates to plasma processing methods such as dry etching, sputtering, and plasma CVD, as well as apparatuses therefor, to be used for manufacture of semiconductor or other electron devices and micromachines. More particularly, the present invention relates to a plasma processing method and apparatus for the use of plasma excited with high-frequency power of VHF or UHF band.
The present invention further relates to a matching box for a plasma processing apparatus to be used for impedance matching in supplying high-frequency power of VHF band, in particular, to a counter electrode for plasma excitation or to an antenna, and relates to a plasma processing method and apparatus using plasma excited with the high-frequency power of VHF band.
Japanese Laid-Open Patent Publication No. 8-83696 describes that the use of high-density plasma is important in order to meet the trend toward microstructures of semiconductors and other electron devices. Furthermore, low electron temperature plasma has recently been receiving attention by virtue of its high electron density and low electron temperature.
In the case where a gas having a high negativity, i.e., a gas that tends to generate negative ions, such as Cl2, SF6, is formed into plasma, when the electron temperature becomes about 3 eV or lower, larger amounts of negative ions are generated than with higher electron temperatures. Taking advantage of this phenomenon makes it possible to prevent etching configuration abnormalities, so-called notch, which may occur when positive charges are accumulated at the bottom of micro-patterns due to excessive incidence of positive ions. This allows etching of extremely micro patterns to be achieved with high precision.
Also, in the case where a gas containing carbon and fluorine, such as CXFy or CxHyFz (where x, y, z are natural numbers), which is generally used for etching of insulating films such as silicon oxide, is formed into plasma, when the electron temperature becomes about 3 eV or lower, gas dissociation is suppressed more than with higher electron temperatures, where, in particular, generation of F atoms, F radicals and the like is suppressed. Because F atoms, F radicals and the like are higher in the rate of silicon etching, insulating film etching can be carried out at larger selection ratios than silicon etching with lower electron temperatures.
Also, when the electron temperature becomes 3 eV or lower, ion temperature and plasma potential also becomes lower, so that ion damage to the substrate in plasma CVD can be reduced.
As a technique capable of generating plasma having low electron temperature, plasma sources using high-frequency power of VHF band or UHF band are now receiving attention.
FIG. 15 is a sectional view of a dual-frequency excitation parallel-flat plate type plasma processing apparatus. Referring to FIG. 15, while the interior of a vacuum chamber 201 is maintained at a specified pressure by introducing a specified gas from a gas supply unit 202 into the vacuum chamber 201 and simultaneously performing evacuation by a pump 203 as an evacuating device, a high-frequency power of 100 MHz is supplied to a counter electrode 205 by a counter-electrode-use-high-frequency power supply 204. Then, plasma is generated in the vacuum chamber 201, where plasma processing such as etching, deposition, and surface reforming can be carried out on a substrate 207 placed on a substrate electrode 206. In this case, as shown in FIG. 15, by supplying high-frequency power also to the substrate electrode 206 by a substrate-electrode-use-high-frequency power supply 208, ion energy that reaches the substrate 207 can be controlled. In addition, the counter electrode 205 is insulated from the vacuum chamber 201 by an insulating ring 211.
FIG. 16 is a sectional view of a plasma processing apparatus which we have already proposed and which has an antenna type plasma source mounted thereon. Referring to FIG. 16, while the interior of a vacuum chamber 301 is maintained at a specified pressure by introducing a specified gas from a gas supply unit 302 into the vacuum chamber 301 and simultaneously performing evacuation by a pump 303 as an evacuating device, a high-frequency power of 100 MHz is supplied to a spiral antenna 313 on a dielectric window 314 by an antenna-use-high-frequency power supply 312. Then, plasma is generated in the vacuum chamber 301 by electromagnetic waves radiated into the vacuum chamber 301, where plasma processing such as etching, deposition, and surface reforming can be carried out on a substrate 307 placed on a substrate electrode 306. In this case, as shown in FIG. 16, by supplying high-frequency power also to the substrate electrode 306 by a substrate-electrode-use-high-frequency power supply 308, ion energy that reaches the substrate 307 can be controlled.
However, there has been an issue that the conventional methods shown in FIGS. 15 and 16 have difficulty in obtaining uniform plasma generation.
FIG. 17 shows results of measuring ion saturation current density at a position just 20 mm above the substrate 207 in the plasma processing apparatus of FIG. 15. Conditions for plasma generation are gas type of Cl2 and gas flow rate of 100 sccm, a pressure of 1 Pa, and a high-frequency power of 2 kW. It can be understood from FIG. 17 that plasma density is higher in peripheral regions.
FIG. 18 shows results of measuring ion saturation current density at a position just 20 mm above the substrate 307 in the plasma processing apparatus of FIG. 16. Conditions for plasma generation are gas type of Cl2 and gas flow rate of 100 sccm, a pressure of 1 Pa, and a high-frequency power of 2 kW. It can be understood from FIG. 18 that plasma density is higher in peripheral regions.
Such nonuniformity of plasma is a phenomenon that could not be seen with the frequency of the high-frequency power of 50 MHz or less. Whereas the 50 MHz or higher high-frequency power needs to be used in order to lower the electron temperature of plasma, there are produced, in this frequency band, not only an advantage that plasma is generated by the counter electrode or antenna being capacitively or inductively coupled to the plasma, but also an advantage that plasma is generated by electromagnetic waves, which are radiated from the counter electrode or antenna, propagating on the surface of the plasma. In peripheral regions of the vacuum chamber, which serve as reflecting surfaces for the electromagnetic waves that have propagated on the surface of the plasma, stronger electric fields are developed so that thick plasma is generated.
Also, as described above, in the case where a gas having a high negativity, i.e., a gas that tends to generate negative ions, such as Cl2, SF6, is formed into plasma, when the electron temperature becomes about 3 eV or lower, larger amounts of negative ions are generated than with higher electron temperatures. Taking advantage of this phenomenon makes it possible to prevent a phenomenon that perpendicularity of the incident angle of ions onto the substrate worsens when positive charges are accumulated at the bottom of micro-patterns due to excessive incidence of positive ions. This allows etching of extremely micro patterns to be achieved with high precision. Besides, that is an expectation for process improvement making use of the high reactivity of negative ions.
Also, in the case where a gas containing carbon and fluorine, such as CxFy or CxHyFz (where x, y, z are natural numbers), which is generally used for etching of insulating films such as silicon oxide, is formed into plasma, when the electron temperature becomes about 3 eV or lower, gas dissociation is suppressed more than with higher electron temperatures, where, in particular, generation of F atoms, F radicals and the like is suppressed. Because F atoms, F radicals and the like are higher in the rate of silicon etching, insulating film etching can be carried out at larger selection ratios than silicon etching with lower electron temperatures.
Also, when the electron temperature becomes 3 eV or lower, ion temperature and plasma potential also become lower, so that ion damage to the substrate in plasma CVD can be reduced.
It is plasma sources using high-frequency power of VHF band that is currently receiving attention as a technique capable of generating plasma low in electron temperature and capable of generating plasma superior in ignitability.
FIG. 24 is a sectional view of a dual-frequency excitation parallel-flat plate type plasma processing apparatus. Referring to FIG. 24, while the interior of a vacuum chamber 401 is maintained at a specified pressure by introducing a specified gas from a gas supply unit 402 into the vacuum chamber 401 and simultaneously performing evacuation by a pump 403 as an evacuating device, a high-frequency power of 100 MHz is supplied to a counter electrode 407 via a matching box 405 and a high-frequency coupling device (mount) 406 by a counter-electrode-use-high-frequency power supply 404. Then, plasma is generated in the vacuum chamber 401, where plasma processing such as etching, deposition, and surface reforming can be carried out on a substrate 409 placed on a substrate electrode 408. In this case, as shown in FIG. 24, by also supplying high-frequency power to the substrate electrode 408 by a substrate-electrode-use-high-frequency power supply 410, ion energy that reaches the substrate 409 can be controlled. In addition, the counter electrode 407 is insulated from the vacuum chamber 401 by an insulating ring 411. The matching box 405 comprises a high-frequency input terminal 412, a first variable capacitor 413, a high-frequency output terminal 414, a second variable capacitor 415, a first motor 416, a second motor 417, and a motor control circuit 418.
However, there has been an issue that the conventional method shown in FIG. 24 has difficulty in obtaining uniform plasma generation.
FIG. 25 shows results of measuring ion saturation current density at a position just 20 mm above the substrate 409 in the plasma processing apparatus of FIG. 24. Conditions for plasma generation are gas type of Cl2 and gas flow rate of 100 sccm, a pressure of 2 Pa and a high-frequency power of 1 kW. Also, as shown in FIG. 24, the second variable capacitor 415 is disposed on one side of the measuring position in FIG. 25. It can be understood from FIG. 25 that plasma density is higher on one side of the measuring position, i.e., just below the second variable capacitor 415.
Such nonuniformity of plasma is a phenomenon that could not be seen with the frequency of the high-frequency power of 50 MHz or less. Whereas the 50 MHz or higher high-frequency power needs to be used in order to lower the electron temperature of plasma, there develops, in this frequency band, a potential distribution in the counter electrode 407. It can be deduced that this potential distribution, affected by the placement of the second variable capacitor 415 within the matching box 405, acts to strengthen the electric fields just below the second variable capacitor 415, resulting in nonuniformity of plasma generation.
Such a phenomenon could be seen with such an arrangement as shown in FIG. 26 in which a spiral antenna 420 is used instead of the counter electrode 407. In the prior art example shown in FIG. 26, a dielectric window 421 is used.